The present invention relates to a method of approaching a probe to a specified place of a sample in a focused microscope or an electron microscope, and to an apparatus for realizing the same.
In the focused microscope or the electron microscope, there is occasionally required an operation for approaching the probe to the specified place of the sample. For example, in a case where, by using a focused ion beam (FIB) apparatus, a minute sample is cut off from the sample such as a wafer and picked up by the probe, it is necessary to confirm whether or not the minute sample has been completely cut off from a sample main body. Further, also when, in order to measure electrical characteristics in a predetermined place of the sample such as a semiconductor device, a manipulator to which the probe has been attached is driven under microscope observation, a needle-like probe tip is directly contacted to an observed portion and the electrical characteristics of the above portion are measured by sending an electric current to a sample piece, there are required confirmations of an approach and a contact of that probe with the observed portion. As a method of confirming that contact, hitherto since a judgement of the contact has been performed by a worker by visually observing a microscope image depicted on a monitor, a detection has been vague. For example, notwithstanding the fact that a portion becoming the sample for a transmission electron microscope (TEM) contacts with a tip part of the probe, there has occasionally existed a case where the confirmation or the detection by the microscope image has been delayed, and such an inconvenience has resulted in that, by such a delay of the detection, the sample for the TEM and a contacting terminal of the probe have been injured by the tip part of the probe. Whereupon as a method of certainly detecting the contact, there is presented such a method that, if a probe voltage is beforehand applied to the probe and, while operating a micro-actuator while microscope-observing it, the probe attached to its tip part is approached to the minute sample to thereby cause a tip of the probe to contact to the sample, since a voltage level changes, this change is made a contact detection signal.
In Patent Document 1, there is disclosed “a focused ion beam apparatus” whose object is to provide an FIB apparatus capable of certainly detecting the contact concerned without providing a new electric source in order to detect the contact between the probe and the sample. As shown in FIG. 6, a probe 1 of this FIB apparatus 101 is grounded through an ammeter 12. When the probe 1 and a sample 5 are being approached by a control of a drive unit 22, an FIB from an FIB barrel 10 is irradiated to the sample 5. At this time, in a case where the probe 1 is not contacting with the sample 5, an electric current generated in the sample 5 by the irradiation of the FIB flows toward an inside of the sample 5. In contrast to this, in a case where the probe 1 is contacting with the sample 5, the electric current generated in the sample 5 flows toward the probe 1. At a point in time at which the probe 1 has contacted with the sample 5, the electric current flowing through the probe 1 increases. It is one in which, by monitoring the electric current flowing through the probe 1 by the ammeter 12, the contact between the probe 1 and the sample 5 is detected from a change quantity of the electric current concerned. That is, it becomes a work in which an operation of the approach is performed while microscope-observing, and the contact is detected by the electric current value change in the ammeter.
Further, as a contact detecting method of the probe, there is presented also a method in which a displacement of a piezoelectric element is monitored as shown in Patent Document 2. For example, in the Patent Document 2, there are presented “a probe unit and a sample operating apparatus using the same” whose object in each is to provide a sample making apparatus or a failure detecting apparatus, which possesses an inexpensive detecting means capable of detecting the contact between the sample and an explorer irrespective of a kind of the sample. This apparatus is one possessing a probe unit in which the explorer which comprises a needle-like electrically conductive material and whose tip has an acute angle shape is fastened to a free end of a strain detecting beam having a piezo-resistance layer whose resistance value changes in compliance with its own displacement, and the other end of the strain detecting beam is retained to a fixed base functioning also as a foundation of the strain detecting beam provided with a conductor part having a current-carrying function for the piezo-resistance layer and the explorer. In this apparatus, there is adopted such a contact detecting method that, if the explorer contacts with the sample, the explorer transmits a strain amount as its reaction to the strain detecting beam and, by the fact that its resistance value has changed, a contact detecting circuit judges the contact between the explorer and the sample. In this method, the operation of the approach is performed while microscope-observing, and the contact is detected by the electric current value change in the ammeter.
Additionally, in Patent Document 3, there are disclosed “a probe driving method and a probe apparatus” whose object in each is to cause the probe to safely and efficiently contact a sample surface by monitoring a probe height. The probe driving method shown in this Document goes through a process in which a charged particle beam is irradiated to a sample image containing a probe image obtained by detecting secondary particles or reflected particles discharged by the charged particle beam irradiation, a distance (1st distance) between a tip position of the probe and a specified position on the sample, and a process in which the charged particle beam is irradiated to the sample and the probe from a 2nd angle different from the 1st angle to thereby find, on the sample image containing the probe image obtained by detecting secondary particles or reflected particles discharged by the charged particle beam irradiation, a distance (2nd distance) between the tip position of the probe and the specified position on the sample, and is an approach in which a distance between the sample and the probe is calculated on the basis of the 1st and 2nd angles and the 1st and 2nd distances, and the probe is driven in a direction of the sample in compliance with the calculated distance between the sample and the probe. In a case where the sample surface is electrically floating, a luminance becomes low due to an electrification by an ion beam irradiation, and the contact can be detected because, if the electrically conductive probe contacts, the charge is dissolved and the image becomes bright. Further, in this Document, there is a description about a method in which a shadow, of the probe, occurring just before contacting to the sample is detected from slightly above beyond the probe, thereby foreseeing an approaching state from a change in contrast.
[Patent Document 1] JP-A-2001-235321 Gazette “FOCUSED ION BEAM APPARATUS, CONTROLLING METHOD OF FOCUSED ION BEAM APPARATUS AND CONTACT DETECTING METHOD”, Laid-Open on Aug. 31, 2001
[Patent Document 2] JP-A-2002-33366 Gazette “PROBE UNIT AND SAMPLE OPERATING APPARATUS USING THE SAME”, Laid-Open on Jan. 31, 2002
[Patent Document 3] JP-A-2002-40107 Gazette “PROBE DRIVING METHOD AND PROBE APPARATUS”, Laid-Open on Feb. 6, 2002
Since the conventional contact detecting method mentioned above is one utilizing a physical phenomenon, such as electrical change or piezoelectric phenomenon, occurring as a result of the contact, it is difficult to cause the probe to approach the sample so as to softly contact therewith while observing. Further, in a case of the electrical change, in a case where a contact object is an insulator, the detection cannot be performed. Also as to an electrically conductive material, there is a case where electrical characteristics are difficult to be obtained because an oxide film is formed on its surface.
Objects of the present invention are to provide a method in which the probe can approach the minute sample so as to certainly and softly contact the sample only by operating the manipulator while microscope-observing without requiring a special detection means, and to provide an apparatus for implementing the same.